Abnormal fuel pressure cut off and purge system



R. R. VOSPER Nov. 16, 1965 ABNORMAL FUEL PRESSURE CUT OFF AND PURGESYSTEM Filed May 5, 1962 QwmOl-o v/ emv Nv llv RALPH R. VOSPER vn/wromUnited States atern:

3,217,782 ABNORMAL FUEL PRESSURE CUT OFF AND PURGE SYSTEM Ralph R.Vosper, Santa Clara, Calif., assignor to Coen Company, Inc., SanFrancisco, Calif. Filed May 3, 1962, Ser. No. 192,263 6 Claims. (Cl.158-132) This invention relates to a safety system for use in connectionwith forced air draft gas burners as may be employed as a source of heatenergy for steam boiler installations, refractory furnaces, or the like.

It is currently normal practice to provide various types of flamefailure safety devices in gas burners to detect and implement correctiveaction in reference to unsafe conditions that may develop with theburner or in the furnace or boiler room. For example, there are variousdevices that are operable to detect extinguishment of the pilot fiame orto detect abnormal high or low pressure fluctuations in the primary gassupply line. Generally speaking, most such safety devices operate toshut off the supply of gas to the burner and to sound a visual or audiowarning signal to the operator so that corrective action can be taken.Although certain components of conventional safety systems are directlyresponsive to, and are actuated by pressure changes in the main gassupply line and/ or in the gas pilot line, all modern safety system ofwhich I am aware depend, at least in part, upon the supply of electriccurrent to actuate electric relays or other electrically actuatedcomponent parts included within the system as a whole.

Although the dependence upon uninterrupted o1' continuous supply of asource of electrical energy to maintain a safety system in operation hasbeen found to be quite satisfactory in many types of boiler or furnaceoperations, it will be realized that in such types of systems should thesource of electric current be stopped or interrupted due to powerfailure, the system will operate in its intended manner to shut off theboiler and extinguish the flame heat source for the boiler. In otherwords, in such types of safety systems, the entire boiler or furnaceoperation can be shut down due to circumstances (i.e., failure ofelectric power supply) that are completely unrelated to the properfunctioning of the burner and boiler room operations per se.

It would appear evident that any optimum safety system should not shutdown the boiler except for causes directly related to some malfunctionof the burner or boiler operation per se. Even in commercial processeswhere the shut down of a boiler will result only in temporary workinterruption and consequent curtailment of productive output, it followsthat any such interruption or curtailment will reflect an economic lossdue to the shutdown. In certain commercial processes, particularly inreference to certain oil refining and/or chemical processes wheretemperatures must be maintained within critical ranges for prolongedperiods of time to properly carry out the process or reaction, even atemporary shutdown of a burner sufficient to cause loss of boilerpressure or heat below the necessary minimum can be of criticalimportance. For example, we are aware of instances in certain oilrefinery processes where even a temporary loss of boiler heat necessaryto maintain the reaction continuously to completion has resulted in thenecessity of throwing away and disposing as waste the raw materialsbeing processed at the time of the shutdown.

A principal object of the present invention is to provide a safetysystem which is not dependent in any way on the supply of electriccurrent or other activating energy sources outside the forced draftair-gas burner system itself. Stated-otherwise, a primary object of theinvention is to provide a safety system which is responsive solely tothe maintenance in the system of a predetermined forced draft combustionair pressure source in conjunction with the maintenance of apredetermined range of minimum low to maximum high pressure in the maingas supply line and in the pilot gas supply line. As will be explainedin more detail hereinafter, a system embodying the present invention isdirectly actuatably responsive to abnormally low and abnormally highpressures in the main gas supply line whereby if the pressure in themain gas supply line should elevate above or drop below thepredetermined safety pressure limits, the said system will operate toshut down the burner. The system is also directly responsive to thecontinued maintenance of forced draft combustion air to the burner andalso to the maintenance of a minimum safety pressure limit beingmaintained in the pilot line whereby if there should be a failure in theforced air draft system, and/ or an abnormal drop of pressure in thepilot gas line, the system will likewise operate to shut off the gassupply to the burner and thereby shut down the system. However, and asabove indicated, none of the safety components incorporated within thepresent system depend upon electric energy being supplied to relays orother electric devices as are normally included in more conventionaltypes of safety systems in current use today. Consequently, theoperation of the present system is not dependent upon, nor will it beaffected by, any electric power failure that may occur in the operatingplant facility.

Other objects are to provide a system of the character briefly mentionedabove which is dependable in operation, relatively simple and economicof construction, and which can be fabricated largely, if not entirely,from commercially available components such as conventional piping,valves and the like.

Other objects of the present invention will become apparent upon readingthe following specification and referring to the accompanying drawingsin which similar characters of reference represent corresponding partsin each of the several views.

In the drawings:

FIG. 1 is a diagrammatic view of a safety system embodying the presentinvention; and

FIG. 2 is a fragmentary diagrammatic view of the master control leverviewed along line 2 2 in FIGURE 1.

Referring more specifically to the draw-ings, it is believed that thepresent system can best be understood by explaining the function of thesystem and its various components during various phases of operation. pconnection, the operation of the system will be first described inreference to a normal startup phase commencing with the purging of thecombustion chamber with air followed by the lighting of the pilot lightand the eventual turning on of the main fuel gas valve. This explanationwill be followed by a further explanation on how the system operateswhen dangerous high and/ or low gas pressure conditions subsequentlyoccur during operation.

Referring to FIGURE 1, main gas control valve 11, the adjustable dampercontrol 12, the purge valve 13, and the low re valve 14, mechanicallyare .all linked or connected to a common master control lever 15 whichis operable to actuate simultaneously all four of the components 11-14in predetermined relation to one another. ln general, when the mastercontrol is moved from its full olf to on positions, both the damper andthe main fuel valve will move from fully closed to fully open positions.The air purge valve 13 and the low tire valve 14 operate insubstantially reverse sequence to one another, in that the low firevalve is only open during the first 20% movement of the master controllever, whereafter further opening movement of the Imaster control willshut off the low fire valve completely; whereas, the purge valve 14 isIn this p opened only during the last 20% opening movement of the mastercontrol lever.

With this interrelation between the main fuel valve, damper, purgevalve, and low fire valve in mind, the system as a whole will now bedescribed. For purposes f such explanation, it may be assumed that thesystem is used in connection with a gas lburner which is installed tointroduce into a combustion chamber and boiler furnace proper a forceddraft air-gas mixture for ignition and flame propagation therein.

Assuming the system is completely shut down and that it is desired tostart it up, the following sequential steps or -acts would be taken:

In order to air-purge the furnace of any raw gas, the fan 21 is startedand the master control lever 15 moved to full on position, which lattermovement will cause the damper 12 and purge valve 13 to fully open, andto cause the low fire valve 14 to close. Although the master controllever is mechanically linked to the main fuel valve, the latter at thisstage of operation will not open to admit gas into the burner fuelsupply line 22. More specifically, until certain other conditions existin the system, particularly such as to actuate fuel valve controldiaphragms 23 and 24, respectively, the manual reset component 11a ofmain fuel valve 11 cannot be operated so .as to open said valve andadmit gas into burner supply line 22. This is so because valve 11 is ofthe type known in the art as a gas shut off safety valve of which `atypical commercial example is given in the table in col. 7, line 70. Invalves of this type the valve stem is caused to physically connect toits operator within a reset component such as that shown at 11a onlywhen fluid pressure is applied land maintained on diaphragms 23 and 24.The source and occurrence of such fluid pressure in my invention is eX-plained in greater detail hereinafter. Mechanical movement of the handleand operator before fluid pressure is applied to diaphragms 23 and 24 isphysically possible in valves of this type but will produce no movementsuch as that of valve 11; this is the condition that prevails duringinitial air purge of the system described herein, prior to firing of thesystem, at which time physical movement of the operator occurs becauseof linkage to handle but no gas passes through valve 11.

With the fan on and the damper open, air will be supplied to the burnerplenum or wind box 26 via air supply conduit 27, and thence flow intothe combustion chamber and boiler furnace to purge any raw gas throughthe furnace exhaust. Means are provided in the present system forestablishing -a predetermined time period during which the purge cyclemust continue before the pilot light can be lit. More specifically, suchmeans includes the purge time needle-valve 28 and volume chamber 29,both of which are located in the pilot air control line 31 which tapsair from the wind box 26. In this connection, valve 28 may comprise aconventional needle valve which can be adjusted to bleed air at apredetermined rate through line 31 into the volume chamber 29. Thus, forexample, if it is desired to establish -a minimum air purge time ofthree minutes (before the pilot valve can be turned on) the needle-valve28 can be adjusted and pre-set to bleed air into chamber 29 at a ratethat will take three minutes before pressure equilibrium between chamber29 and the wind box is established. (The length of time that it takesfor pressure equilibrium to be reached is primarily a function of thecross-sectional opening of the needle valve and the volume of thechamber 29.) When pressure equilibrium between chamber 29 and the windbox 26 has been established, air from the volume chamber will flowthrough pilot opening valve 32 which, as indicated, is a three-way valveand has la com-mon port, a normally open port, and a normally closedport designated respectively by the letter reference characters C(common port), NO (normally open port), and NC (normally closed port).As further indicated, the common port and normally open port of valve 32establish normal straight-through communication in line 31, whereas,when the valve is actuated by pressure diaphragm responsive means 32a(to be referred to more specifically hereinafter), the normally closedport is opened so as to vent pressure in line 31 to atmosphere.

Valve 32, as well as valves 33, i2 and 43, referred to hereinafter, isof the type known in the art as a pressure controller valve of which atypical commercial example found to be satisfactory for my invention islisted in the table in col. 7, lines 65 thru 69. When diaphragm 32a (or33a, 42a, or 43a of the other valves referred to) has an external fluidpressure applied to it, the three way porting of valve 32 itself isshifted by the action of the diaphragm moving -a valve plunger whichcauses the port changes indicated on the accompanying drawing andreferred to herein-after. When the external fluid pressure is removedfrom the diaphragm, the valve returns to its former porting position.

At this stage of operation, after the full minimum purge time haselapsed, it may 4be assumed that the operator willl move the mastercontrol 15 to low starting fire position,- which said movement will: (l)cause the damper 12 to substantially close, (2.) cause the purge valve13 to close, (3) cause the main fuel valve 11 to correspondingly movetoward closed position, and (4) cause low re valve 14 to open. Openingof low fire valve 14 will establish air ow communication from volumechamber 29 through the air line 31 and through the normally open andcommon ports of pilot-sustaining valve 33 into the pressureresponsivevalve actuator 34a of the manual reset gas pilot control valve 34.Previously mentioned pilot sustaining valve 33 is a pressure responsivethree-way valve -substantially identical to pilot opening valve 32.Valve 33 includes a pressure responsive actuator 33a which Will bereferred to more specifically hereinafter.

The assembly comprising valve 34, reset component 34h and actuator ordiaphragm 34a are known expedients in the valve art of which a typicalcommercial example is listed in the table in col. 7, line 60. Such avalve may be physically shifted by handle 34e to permit passage of a uidthrough its body only after fluid pressure is applied to diaphragm 34a,which fluid pressure causes movement of said diaphragm and operativeengagement of the valve operator with the valve stem. After such fluidpressure is removed, valve 34 returns to its original or closedposition. The referred to fluid pressure is obtained and applied asexplained in detail below.

When air pressure is established between volume chamber 29 and thepressure actuator 34a, the lmanual reset component 3411 of pilot valve34 is placed in lan operable condition whereby the pilot valve turn-onhandle 34C can be manually opened to turn on the pilot gas leading tothe pilot light in the burner via pilot gas supply line 35. On thedownstream side of pilot valve 34 are three gas pressure controltake-off lines indicated at 36, 37, and 40, respectively, which areconnected respectively to the pressure responsive valve actuator meanspreviously designated at 241, 32a and 33a.

More specifically, gas pressure in line 36 will actuate pressureresponsive diaphragm 24 of the main fuel valve 11. This alone will notrender valve 11 in a condition to open and permit flow of gas throughsupply line 22, because it is also necessary that for valve 11 to berendered operative to open pressure, responsive diaphragm 23 must alsobe actuated under influence of air pressure in the primary air conduit2'7 leading from the fan 21 to the damper 12 and through branches 38 and38a to the chamber in communication with Said responsive diaphragm 23.It is seen that lines 3S and 38a are normally open to establish constantair pressure to diaphragm actuator 23 during all stages and conditionsof operation, except in the single instance where there is developeddangerously high gas pressure in line 22. The operat-ion of the systemwhere this latter condition develops will be explained hereinafter.

Pressure control line 37 actuates the pressure responsive diaphragm 32awhich will cause actuation of pilot opening valve 32, whereby thenormally open port will be closed and the normally closed port will bevented to atmosphere. The valve will be held in this latter position aslong as normal pilot gas pressure continues to flow through pilot gassupply line 35. When valve 32 is actuated as above described, it is seenthat air flow from the volume charnber side of line 31 is shut off, andany residual air on the downstream side of valve 32 is bled toatmosphere from the line by low fire control bleed valve 39.

Moreover, bleed valve 39 is pre-set to a slightly open condition so thatvolume chamber 29 is relieved of its pressure after a given safe timeinterval. This causes relief of pressure on actuator 34a and preventspilot valve 34 from being actuated after a predetermined periodsubsequent to purging. This insures that pilot gas pressure must beinitiated promptly after a given purge procedure has been carried out;otherwise the operation of start up must be reinitiated. This gives theadded safety feature of not permitting valve 34 from being actuable foran indefinitely long period of time after purging. The amount that valve39 is left open, however, is small in relation to the normal air flowbetween chamber 29 and actuator 34a so that the constant bleeding thatis inherent does not interfere with nor prevent normal operation afterpurging if done within a reasonable time. Valve 39 is a globe type valveof any manufacturer and a well-known expedient in the valve art.Pressure within the pressure responsive valve actuator 34a suicient tomaintain gas pilot valve 34 open is continued to be maintained by airpressure from the fan 21 as supplied via conduit 41 and pilot sustainingvalve 33. More specifically, simultaneously with the actuation of valve32 to shut off volume chamber pressure to valve 34 as aforesaid, valve33 will also be actuated by virtue of pilot gas line pressure acting onpressure responsive valve means 33a via pressure control line 40. Morespecifically, the pressure responsive diaphragm 33a will cause valve 33to actuate whereby the normally open port will close and the normallyclosed port will open, whereby air communication between line 31 and thepressure responsive component of pilot valve 34 is closed and wherebysimultaneously direct air pressure communication between the fan 21 andthe `said pilot valve 34 is open via line 41. During normal operation ofthe burner, air pressure from the fan via conduit 41 and through valve33 will maintain actuating and holding pressure sufficient to keep thepilot valve open, and whereby gas continues to flow to the pilot lightin the burner.

Briefly recapitulating certain portions of the foregoing explanation itis seen that as long as the burner continues to operate within normalranges and conditions of maximum and minimum gas pressures, air and fuelgas will be supplied and controlled by regulation of the master controllever which, as above explained, vsimultaneously controls the air damperand the opening and closing movements of the main fuel valve. Obviously,the amount of fuel and air supplied would be related to and dependentupon the particular load requirements and capacity of the burnerrequired during its operating cycle. In other words, as long as the maingas pressure in the supply line 22 is maintained within normalpredetermined high and low pressure operating limits (conditional alsoupon continued supply of air pressure in the system from fan or blower21), the components of the system hereinabove described will continue tomaintain both the pilot valve 34 and the main fuel valve open.

In the event that the gas pressure in line 22 should elevate above apredetermined safety pressure level, high gas pressure safety controlvalve 42 will actuate to close the main fuel valve 11; whereas, shouldpressure in line 22 drop below a predetermined minimum safety level, lowgas pressure safety control valve 43 will be caused to actuate and shutolf both the main fuel valve as well as the pilot gas valve.

More specifically, if and when gas pressure in line 22 should exceed apredetermined safety limit, such pressure will be sensed by the pressureresponsive actuator 42a of the high pressure safety control valve 42. Inthis connection, pressure responsive actuator 42a is directly connectedto the downstream side of the fuel line 22 via gas pressure tap line 44.High pressure actuation of valve 42 will cause the normally plugged portto vent to atmosphere whereby air pressure in lines 38 and 38a will bebled and which in turn will result in the loss of pressure againstpressure responsive diaphragm 23 associated with the fuel valve 11. Aspreviously explained, in order for the fuel valve to be opened, 0r toremain open, it is necessary that both the pressure responsive diaphrams23 and Z4 be actuated by their respectively associated pressure sources.When either of the diaphrams 23 or 24 becomes de-actuated, the main fuelvalve will automatically close and prevent further supply of fuel gas tothe burner until the condition causing the shut down of the system isremedied. Generally speaking, high pressure gas will develop in the linedue to pressure fluctuations at the primary source of fuel supply and/ordue to failure of pressure regulators normally provided in the supplyline.

As previously indicated, should pressure in main gas line 22 drop belowthe predetermined minimum safety level, low gas pressure safety controlvalve 43 will operate to cause both the main fuel valve 11 and the pilotvalve 34 to shut o. More specifically, in normal operations where thepressure in line 22 is maintained above its predetermined safety limit,gas pressure, tapped from line 22 via conduit 46, will act upon thepressure responsive component 43a of the said valve 43 to maintain thevalve parts in their position of operation shown in FIG. 1 of thedrawings. More specifically, it will be observed that valve 43 is shownwith a common port C connected to air tap line 41 and is also shown withnormally open and normally closed ports designated by the referencecharacters NO and NC respectively. The port indicated at NC is pluggedto atmosphere, and the normally open port is vented to atmosphere.During normal burner operations, pressure tapped from line 22 via line46 will act upon pressure responsive valve component 43a to cause thevalve element of valve 43 to rotate in the direction of the arrow shownwhereby the normally open port will be plugged to prevent venting ofpressure in air tap line 41 to atmosphere, whereby air pressure in saidtap line 41 will continue to be transmitted via pilot sustaining valve33 to the pressure responsive component 34a of pilot valve 34 tomaintain the latter valve Open as heretofore explained. When, however,pressure in main gas line 22 drops below the predetermined minimumsafety level, such pressure drop will be sensed by the pressureresponsive component 43a of valve 43 which, in turn, will causeactuation of the valve element to its position shown in the drawings,and whereby air from tap line 41 will be vented to atmosphere throughthel normally open port. This will cause an immediate correspondingpressure loss in tap line 41 which, in turn, will be sensed by thepressure responsive component 34a of pilot valve 34 to cause the lattervalve to shut off. Closing of the pilot valve, in turn, will result in asubstantially immediate loss of pressure in pilot gas supply line 35 andin the three pressure take-off lines 36, 37 and 40, respectively. Lossof pressure in take-olf` line 36 will deactuate pressure responsivediaphragm 24 and cause the main fuel valve 11 to shut olf. Loss ofpressure in line 37 will deactuate the pressure responsive component 32aof pilot opening valve 32 and return the valve parts to their positionshown in the drawings as they exist at the moment of start-up of anoperating cycle as earlier explained. Simlarly, loss of pressure intake-off line 40 will deactuate pressure responsive component 33a ofpilot sustaining valve 33 and likewise cause the valve parts to Y returnto their start-up position as shown in the drawings and as also earlierdescribed.

From the foregoing it may be noted that the closing of the fuel valve 1ldue to high pressure gas conditions as above described will not effectthe pilot gas valve and pilot gas will continue to be supplied to theburner even during the shutdown of the main fuel valve because of highpressure gas conditions. It therefore follows that if and when the mainfuel valve should be automatically shut off due to high pressure gasconditions, it is unnecessary to go through the steps of either shuttingoff the pilot or of purging the furnace with air before the main fuelvalve can again be turned on in order to continue normal operationsafter alleviation of the high pressure gas conditions in the line. Onthe other hand, a different situation is true when both the main fuelValve and pilot valve are shut off due to the development of a lowpressure gas condition in the system, the happening of which willnecessitate that an operator go through the necessary air purging stepspreviously described before he can turn on either the pilot or the mainfuel valve. This is an intentional safety measure which is built intothe present system to prevent any possibility of prematurely lightingthe burner with raw gas present after low gas pressure failure hascaused it to shut down.

Air purging is unnecessary after failure of the main gas alone due to ahigh pressure condition since the pilot having remained unextinguishedwill ignite any gas introduced at the burner at a later time by the maingas supply line. Thus no unignited gas mixture may collect within thecombustion chamber to cause a dangerous explosive condition. This ofcourse is not the case where there has been failure of the pilot alonedue to low pressure or loss of pressure in the pilot line. This is sobecause under the latter circumstances, after the pilot has beenextinguished, large quantities of gas may be introduced in the system byfaulty admission of gas conveyed by low level pilot pressure and/orfaulty introduction of gas to the combustion chamber from the main gasline. In such event, permitting firing of the pilot line with normaloperating pressures before an air purge could result in a damagedexplosion.

The present system, and the various components thereof have beenillustrated schematically in the drawings. It is pointed out that asystem embodying the present invention can be fabricated from parts andequipment that are per se known in the art and that can be purchasedfrom existing market sources. It is believed apparent that the air linesand gas lines comprising the system involve conventional plumbing.Likewise, the various types of pressure responsive valves that are usedin the system can be of known types. In this connection and in order toprovide more complete practical information as to how the presentinvention may be practiced, the following manufacturing sources fromwhence certain designated component parts may be purchased arehereinbelow listed:

Name 0f component Part No. Name of manufacturer Manual reset Locktitevalve, manufactured by Eclipse Fuel Engineering Co., Rockford, Illinois.

Pilot valve Pilot opening valve 32 Pilot sustaining valve High pressuregas supply valve. Low pressure gas supply valve Main fuel valve Theforegoing manufacturing sources are given only to indicate that thevarious types of pressure sensitive 8 valves used in the system may bepurchased commercially from existing manufacturing sources. It isunderstood, that the present invention does not depend upon the usehowever, of any particular brand of manufactured item and that thecomponents can be purchased from other manufacturers than those abovelisted, or can be fabricated especially for their intended purposewithin the present system.

Although the foregoing invention has been described in some detail byWay of illustration and example for purposes of clarity ofunderstanding, it is understood that certain changes and modificationsmay be practiced within the spirit of the invention as limited only bythe scope of the appended claims.

I claim:

ll. ln forced draft air-gas burners utilizing a main gas supply lineincluding a pressure responsive manual reset main gas valve, a primaryair source, and a pilot gas supply line including a manual resetpressure response pilot valve, a safety system comprising: meansconnecting said pressure response pilot valve to be responsive to airpressure of said primary air source to permit said pilot valve to bemanually opened and permit gas flow therethrough into said pilot gassupply line; means connecting said pressure responsive main gas valve tobe responsive to pressure in said pilot gas supply line and alsoresponsive to air pressure from said primary air source to permitopening of said main gas valve and establish gas flow in said main gassuplpy line, a high gas pressure sensing valve, means connecting saidhigh gas pressure sensing valve to be responsive to unsafe high pressurein said main gas supply line to shut-off air pressure from said primaryair source to said rnain gas valve; said main gas valve through itsconnecting means arranged to be responsive to shut-off of air pressurefrom said primary air source to close said main gas valve and shut-olfsupply of gas through said main gas supply line; a low gas pressuresensing valve means Operably responsive to unsafe low pressure in saidmain gas supply line to shut olf air pressure from said primary airsource to said pilot valve to cause the latter to close and shut offsupply of pilot gas line pressures to said main gas valve and therebycause said latter valve to close and shut olf supply of gas to said maingas supply line.

2. The combination of claim l and including air purge timing meansoperable to require the primary air source to operate for apredetermined minimum time limit and to supply forced draft air to thesystem before said pilot gas valve can be opened.

3. The combination of claim 2 and wherein said air purge timing meansincludes an air purge control line; a bleeder valve in said air purgecontrol line; an air reservoir chamber immediately downstream from saidbleeder valve and in fluid Comunication with said primary air sourcethrough said bleeder valve and said air purge control line; said bleederoperable to admit air from said source to said chamber at apredetermined rate whereby a predetermined time delay is required forair pressure to develop within the said chamber sufficient to cause saidsaid pressure responsive pilot Valve to be opened after said primarysource develops said air pressure and is shut off from said chamber.

4l. The combination of claim 3 and wherein said air purge control linefurther includes a pressure responsive pilot opening valve and athree-way pressure responsive pilot sustaining valve both located on thedownstream side of said reservoir chamber; said pilot opening valvenormally open to admit air through said control line and through thenormally open sustaining valve to said pilot valve to permit the latterto be manually opened as aforesaid; the pressure responsive component ofsaid pilot opening valve connected to said pilot gas supply line andresponsive to pressure in said pilot gas supply line to close offfurther air ow through said control line to said pressure responsivepilot valve; the normally closed port of said pilot sustaining valveconnected to said primary air source and the pressure responsivecomponent of said sustaining valve connected to said pilot gas supplyline and operable under iniiuence of such pressure to open said normallyclosed port to admit air flow therethrough from said air source to saidpressure responsive pilot valve to maintain the latter open when thepilot opening valve closes as aforesaid.

5. In forced draft air-gas burners utilizing a main gas supply line, aprimary air source, and a pilot gas supply line, a safety systemresponsive to predetermined limits of unsafe low and high gas pressurein said gas supply line comprising: a pressure responsive gasturn-on-valve arranged to open and close gas communication through saidmain gas supply line; first pressure responsive safety means associatedwith said gas turnaon valve and operable to sense and unsafe highpressure condition in said gas supply line and cause said turn-on valveto close; second pressure responsive safety means associated With saidgas turn-on valve operable t0 sense an unsafe 10W pressure condition insaid pilot gas supply line and cause said turnon Valve to close.

6. The combination of claim 5 and wherein a pilot in said pilot gassupply line and said gas turn-on valve includes a first pressureresponsive component sensitive to pressure from said primary air sourceand also includes a second pressure responsive component sensitive topressure in said pilot gas supply line; said gas turn-on valveconstructed so as to close upon loss of pressure acting on either of itsfirst and second pressure components; said irst safety pressureresponsive means including a valve operable upon a condition of unsafehigh gas pressure in said main gas line to close ofrr air communicationfrom said air source to said first component of said gas turn-on valveand thereby cause the latter to close; said second safety pressureresponsive means including means operable upon a low gas pressurecondition occurring in said main gas line to close said pilot valve andthereby shut oit pilot gas line pressure to said second compOnent ofsaid gas turn-on valve and thereby cause said turn-on valve to close.

References Cited by the Examiner UNITED STATES PATENTS 907,103 12/1908Bowman 137-458 2,467,357 4/1949 Ioesting 236--1 2,622,669 12/ 1952Caracristi et al. 2,688,337 9/1954 Shivers. 3,018,791 1/1962 Knox137-458 FOREIGN PATENTS 594,601 3/1960 Canada.

JAMES W. WESTHAVER, Primary Examiner.

FREDERICK KETTERER, Examiner.

1. IN FORCED DRAFT AIR-GAS BURNERS UTILIZING A MAIN GAS SUPPLY LINEINCLUDING A PRESSURE RESPONSIVE MANUAL RESET MAIN GAS GALVE, A PRIMARYAIR SOURCE, AND A PILOT GAS SUPPLY LINE INCLUDING A MANUAL RESETPRESSURE RESPONSE PILOT VALVE A SAFETY SYSTEM COMPRISING: MEANSCONNECTING SAID PRESSURE RESPONSE PILOT VALVE TO BE RESPONSIVE TO AIRPRESSURE OF SAID PRIMARY AIR SOURCE TO PERMIT SAID PILOT VALVE TO BEMANUALLY OPENED AND PERMIT GAS FLOW THERETHROUGH INTO SAID PILOT GASSUPPLY LINE; MEANS CONNECTING SAID PRESSURE RESPONSIVE MAIN GAS VALVE TOBE RESPONSIVE TO PRESSURE IN SAID PILOT GAS SUPPLY LINE AND ALSORESPONSIVE TO AIR PRESSURE FROM SAID PRIMARY AIR SOURCE TO PERMITOPENING OF SAID MAIN GAS VALVE AND ESTABLISH GAS FLOW IN SAID MAIN GASSUPPLY LINE, A HIGH GAS PRESSURE SENSING VALVE MEANS CONNECTING SAIDHIGH GAS PRESSURE SENSING VALVE TO BE RESPONSIVE TO UNSAFE HIGH PRESSUREIN SAID MIAN GAS SUPPLY LINE TO SHUT-OFF AIR PRESSURE FROM SAID PRIMARYAIR SOURCE TO SAID MAIN GAS VALVE; SAID MAIN GAS VALVE THROUGH ITSCONNECTING MEANS ARRANGED TO BE RESPONSIVE TO SHUT-OFF OF AIR PRESSUREFROM SAID PRIMARY AIR SOURCE TO CLOSE SAID MAIN GAS VALVE AND SHUT-OFFSUPPLY OF GAS THROUGH SAID MAIN GAS SUPPLY LINE; A LOW GAS PRESSURESENSING VALVE MEANS OPERABLY RESPONSIVE TO UNSAFE LOW PRESSURE IN SAIDMAIN GAS SUPPLY LINE TO SHUT OFF AIR PRESSURE IN SAID PRIMARY AIR SOURCETO SAID PILOT VALVE TO CAUSE THE LATTER TO CLOSE AND SHUT OFF SUPPLY OFPILOT GAS LINE PRESSURE TO SAID MAIN GAS VALVE AND THEREBY CAUSE SAIDLATTER VALVE TO CLOSE SAID SHUT OFF SUPPLY OF GAS TO SAID MAIN GASSUPPLY LINE.